Ford Fiesta 1994, battery light went on?

i have a ford fiesta 1994 (german model)
today for no apperent reason the battery light lit and wouldn't turn off, the car is functional, and i can see nothing wrong with it, but still it troubles me.
could it be that the battery doesn't charge?
could it be just bad electricity that short circuit the light?
any help will be welcomed
thanks
Dror